LinkExtension.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace Extensions
{
    public static class LinkExtension
    {
        public static string Linkify(this string text, string target = "_self")
        {
            Regex domainRegex = new Regex(@"(((?<scheme>http(s)?):\/\/)?([\w-]+?\.\w+)+([a-zA-Z0-9\~\!\@\#\$\%\^\&amp;\*\(\)_\-\=\+\\\/\?\.\:\;\,]*)?)", RegexOptions.Compiled | RegexOptions.Multiline);

            return domainRegex.Replace(
                text,
                match => {
                    var link = match.ToString();
                    var scheme = match.Groups["scheme"].Value == "https" ? Uri.UriSchemeHttps : Uri.UriSchemeHttp;

                    var url = new UriBuilder(link) { Scheme = scheme }.Uri.ToString();

                    return string.Format(@"<a href=""{0}"" target=""{1}"">{2}</a>", url, target, link);
                }
            );
        }


    }
}